code: def _straight_through_backward(grad_output, x):
      return grad_output
  
file_path: advertorch/tests/test_bpda.py
imports: import itertools
  import pytest
  import torch
  import torch.nn
  from advertorch.bpda import BPDAWrapper
  from advertorch.utils import torch_allclose
  from advertorch.test_utils import withgrad_defenses
  from advertorch.test_utils import nograd_defenses
  from advertorch.test_utils import defense_kwargs
  from advertorch.test_utils import defense_data
  from advertorch.test_utils import vecdata
label_desc: Use image node_id 2 for calling a global function with example usage: _straight_through_backward(grad_output, x) and returns: grad_output